Sparse columns REDUCE the space needed not negates: Sparse columns reduce the space requirements for null values at the cost of more overhead to retrieve nonnull values.http://msdn.microsoft.com/en-us/library/cc280604.aspx

http://msdn.microsoft.com/en-us/library/cc280604.aspx Specifically from the link above, a little aways below the 'less space' item quoted in the thread above, you find this (emphasis added)

The SQL Server Database Engine uses the SPARSE keyword in a column definition to optimize the storage of values in that column. Therefore, when the column value is NULL for any row in the table, the values require no storage.

So if you read the details, the 'reduction' for storing null values is apparently 100% 'eliminate' would perhaps have been a more accurate word for them to use than 'reduce', since most of us think of reduce as being less than a 100% modification.. Still since it's proper to speak of 'reducing a price to zero' I believe it's technically grammatically correct to say 'reduce' in that instance, and NOT a conflict to then later in the same document spell out the extent of the reduction being 100%.

The sparse column itself requires no space for storage if it contains a null value. However, additional storage space is required to store non-null values in the sparse column. That's why you don't get a 100% total space savings. In some cases the savings is pretty low.

skjoldtc (2/20/2009)The sparse column itself requires no space for storage if it contains a null value. However, additional storage space is required to store non-null values in the sparse column. That's why you don't get a 100% total space savings. In some cases the savings is pretty low.

That's exactly as I understand it. The books-online stuff actually gives the approximate level of 'sparseness' (as it were) needed to achieve a 40% space savings.. So yeah a 'sparse' column that isn't actually sparsely populated with cells that contain non-null values, could very easily use more space.

I think the question however was as to the tickbox for the item that said that storing a null in a sparse column uses zero space, which based on the docs referenced above is TRUE